4. Environmental Setting, Impacts, and Mitigation Measures 4.E Noise Introduction This section summarizes information on the noise environment in the St. Helena planning area and provides an evaluation of the noise-related effects of the proposed General Plan Update. The analysis considers existing and projected noise along major roadways, in addition to other noise sources in the area. Mitigation measures are recommended that address General Plan Update policies and implementing actions. The noise element of a city’s general plan is a comprehensive approach for including noise control in the planning process. It is a tool for achieving and maintaining environmental noise levels that are compatible with specific land use types. The Public Health, Safety and Noise Element of the proposed General Plan Update identifies noise-sensitive land uses and noise sources, defines areas of noise impact, and establishes goals, policies, and implementing actions to protect people from excessive noise and vibration. Setting Background Information on Noise Noise may be defined as unwanted sound. Noise is usually objectionable Noise is defined as unwanted because it is disturbing or annoying. The objectionable nature of sound could sound. be caused by its pitch or its loudness. Pitch is the height or depth of a tone or sound, depending on the relative rapidity (frequency) of the vibrations by which it is produced. Higher pitched signals sound louder to humans than sounds with a lower pitch. Loudness is intensity of sound waves combined with the reception characteristics of the ear. Intensity may be compared with the height of an ocean wave in that it is a measure of the amplitude of the sound wave. In addition to the concepts of pitch and loudness, there are several noise measurement scales that are used to describe noise in a particular location. A decibel (dB) is a unit of measurement that indicates the relative amplitude of a sound. The zero on the decibel scale is based on the lowest sound level that the healthy, unimpaired human ear can detect. Sound levels in decibels are calculated on a logarithmic basis. Thus, an increase of 10 decibels represents a ten-fold increase in acoustic energy, while 20 decibels is 100 times more intense, 30 decibels is 1,000 times more intense, and so on. There is a relationship between the subjective noisiness or loudness of a sound and its intensity. Each 10-decibel increase in sound level is perceived as approximately a doubling of loudness over a fairly wide range of intensities. Technical terms are defined in Table 4.E-1. St. Helena General Plan Update 4.E-1 May 2016 Revised Draft EIR 4. Environmental Setting, Impacts, and Mitigation Measures E. Noise TABLE 4.E-1 DEFINITIONS OF ACOUSTICAL TERMS Term Definitions Decibel, dB A unit describing, the amplitude of sound, equal to 10 times the logarithm to the base 10 of the ratio of two like quantities. Sound Pressure Level Sound pressure is the sound force per unit area, usually (SPL) expressed in micro Pascals (or 20 micro Newtons per square meter), where 1 Pascal is the pressure resulting from a force of 1 Newton exerted over an area of 1 square meter. The sound pressure level is expressed in decibels as 20 times the logarithm to the base 10 of the ratio between the pressures exerted by the sound to a reference sound pressure (e.g., 20 micro Pascals).Ten times the logarithm to the base 10 of the ratio between the square of the sound to the square of the reference sound pressure of 20u Pascals Sound pressure level is the quantity that is directly measured by a sound level meter and expressed in dB. Frequency, Hz The number of complete pressure fluctuations per second above and below atmospheric pressure. Normal human hearing is between 20 Hz and 20,000 Hz. A-Weighted Sound The SPL in decibels as measured on a sound level meter using Level, dBA the A-weighting filter network. The A-weighting filter de- emphasizes low and high frequency components of the sound in a manner similar to the frequency response of the human ear. Noise Unwanted or unhealthful sound. Equivalent Noise Level, The average A-weighted sound level during the measurement Leq period. The A-weighted equivalent continuous sound level Lmax, Lmin The maximum and minimum A-weighted sound level during the measurement period with the sound meter using the fast time weighting. L01, L10, L50, L90 The A-weighted sound levels that are exceeded 1%, 1 %, 50 %, and 90 % of the time during the measurement period. Day/Night Noise Level, The average A-weighted sound level during a 24-hour day, Ldn or DNL obtained after the addition of 10 decibels to levels measured at night between 10:00 pm and 7:00 am. Total Sound The composite of sound from all sources, near and far. Ambient Sound The sound level measured in the absence of an intrusive or extraneous noise. Intrusive Noise The noise from a source of specific origin which intrudes above the existing background sound level. The degree of intrusiveness of a sound depends upon its amplitude, duration, frequency, time of occurrence and tonal or informational content as in contrast to the prevailing background sound level which exists in the absence of the intrusive noise. Background Sound The LA90 of the ambient sound. It represents the ever-present Level lower sound level due to distant sources which are individually indistinguishable, and in the absence of the intrusive or extraneous noise. Extraneous Noise Specific or distinguishable intermittent sound. It represents sound from nearby sources such as mechanical devices, leaf blowers, pumps, horns, sirens, barking, shouting, birds, wind and other similar individual sources, which don’t normally exist on a continuous or regular basis. SOURCE: Handbook of Acoustical Measurements and Noise Control, Harris, 1998. St. Helena General Plan Update 4.E-2 May 2016 Revised Draft EIR 4. Environmental Setting, Impacts, and Mitigation Measures E. Noise There are several methods of characterizing sound. The most common in California is the A-weighted sound level or dBA. This scale gives greater weight to the frequencies of sound to which the human ear is most sensitive. Representative outdoor and indoor noise levels in units of dBA are shown in Table 4.E-2. Because sound levels can vary markedly over a short period of time, a method for describing either the average character of the sound or the statistical behavior of the variations must be used. Most commonly, environmental sounds are described in terms of an average level that has the same acoustical energy as the summation of all the time-varying events. This energy-equivalent sound/noise descriptor is called Leq. The most common averaging period is hourly, but Leq can describe any series of noise events of arbitrary duration. The scientific instrument used to measure noise is the sound level meter. Sound level meters can accurately measure environmental noise levels to within about plus or minus 1 dBA. Various computer models are used to predict environmental noise levels from sources, such as roadways and airports. The accuracy of the predicted models depends upon the distance the receptor is from the noise source. Close to the noise source, the models are accurate to within about plus or minus 1 to 2 dBA. Since the sensitivity to noise increases during the evening and at night – because excessive noise interferes with the ability to sleep – 24-hour descriptors have been developed that incorporate artificial noise penalties added to quiet-time noise events. The Community Noise Equivalent Level, CNEL, is a measure of the cumulative noise exposure in a community, with a 5-dB penalty added to evening (7:00 PM - 10:00 PM) and a 10 dB-addition to nocturnal (10:00 PM - 7:00 AM) noise levels. The Day/Night Average Sound Level, DNL or Ldn, is essentially the same as CNEL, with the exception that the evening time period (7 p.m to 10 p.m) is dropped and all occurrences during this three-hour period are grouped into the daytime period. Effects of Noise Sleep and Speech Interference The thresholds for speech interference indoors are about 45 dBA if the noise Steady noise of sufficient is steady and above 55 dBA if the noise is fluctuating. Outdoors, the intensity (above 30 dBA) and thresholds are about 15 dBA higher. Steady noise of sufficient intensity fluctuating noise levels above about 45 dBA have been shown (above 30 dBA) and fluctuating noise levels above about 45 dBA have been to affect sleep. shown to affect sleep. Typically, the highest steady traffic noise level during the daytime is about equal to the Ldn and nighttime levels are 10 dBA lower. St. Helena General Plan Update 4.E-3 May 2016 Revised Draft EIR 4. Environmental Setting, Impacts, and Mitigation Measures E. Noise The interior noise standard for multi-family dwellings is set by the State of California at 45 dBA Ldn. The standard is designed for sleep and speech TABLE 4.E-2 TYPICAL NOISE LEVELS IN THE ENVIRONMENT Common Outdoor Activities Noise Level (dBA) Common Indoor Activities Jet fly-over at 1,000 feet 110 dBA Rock band Gas lawn mower at 3 feet 100 dBA Food blender at 3 feet Diesel truck at 50 feet at 50 mph 90 dBA Garbage disposal at 3 feet Noisy urban area, daytime 80 dBA Vacuum cleaner at 10 feet Gas lawn mower, 100 feet 70 dBA Normal speech at 3 feet Commercial area Heavy traffic at 300 feet 60 dBA Large business office Quiet urban daytime 50 dBA Dishwasher in next room Quiet urban nighttime 40 dBA Theater, large conference room Quiet suburban nighttime 30 dBA Library Bedroom at night, concert hall Quiet rural nighttime 10 dBA (background) 0 dBA SOURCE: Technical Noise Supplement (TeNS), Caltrans, September 2013.